Process of oxidative catalytic dehydrocyclization of substituted aromatic compounds

ABSTRACT

INDOLES, BENZOTHIOPHENES AND BENZOFURANS ARE PREPARED BY OXIDATIVE DEHYDROCYCLIZATION OF SUBSTITUTED AROMATIC COMPOUNDS IN THE PRESENCE OF AN OXYGEN-CONTAINING GAS AND AN ACTIVATED SILICA CATALYST.

United States Patent US. Cl. 260319.1 9 Claims ABSTRACT OF THE DISCLOSURE Indoles, benzothiophenes and benzofurans are prepared by oxidative dehydrocyclization of substituted aromatic compounds in the presence of an oxygen-containing gas and an activated silica catalyst.

The present invention relates to a process of oxidative catalytic dehydrocyclization of substituted aromatic compounds in order to produce heterocyclic compounds containing oxygen, nitrogen or sulphur atoms in their heterocyclic ring.

Particularly the process according to the present invention may be used to produce indole from o-ethylaniline, benzofuran from o-ethylphenol, benzothiophene from oethylthiophenol and their derivatives starting from the corresponding substituted aromatic compounds.

Many interesting heterocyclic compounds have been synthesized but the methods for their preparation often employ very expensive raw materials and/or catalysts and base on difiicult processes which often give rise to very low yields of the final product.

Some catalytic dehydrocyclization process of alkyl-substituted aromatic compounds have recently been proposed, particularly in order to produce indole from o-ethylaniline, which processes employed as catalysts cobalt molybdates or platinum or palladium on activated alumina carrier.

However the above processes have the disadvantage of a very high cost of the catalyst and of its very fast deactivation, owing to the formation of very high amounts of coke, which necessarily require frequent regenerations.

The object of the present invention consists in obtaining high yields of heterocyclic compounds by means of simple and cheap processes; particularly it consists in providing a cheap method for the synthesis of indole, benzofuran and benzothiophene, in which both the reaction product is obtained with very high selectivity and the formation of undesirable by-products like polymers and pitches is avoided.

According to the process of the present invention, a mixture of a substituted aromatic compound and oxygen, or a gas containing oxygen, is forced to pass through a reactor at high temperature and, according a preferable way of carrying it out, in presence of steam or any other inert diluent, on a catalyst essentially comprising activated silica, or a mixture of oxides of antimony and of a metal selected from the ones of the 3rd, 4th, 6th and 8th group of the periodic system, or a bismuth, molybdenum and vanadium base ternary compounds.

The aforesaid process can be carried out on many substituted aromatic compounds, which can be exemplified by the following general formula:

wherein R may be an alkyl radical with at least two carbon atoms; R may be hydrogen, an alkyl or an aryl radi- 3,773,784 Patented Nov. 20, 1973 ICC cal, a nitro-, halogen-, cyano-, amino-, alkoxy-, OH, SH, SO H group, or may be a divalent radical giving rise to a condensed ring; Y may be a member of the group consisting of --OH, SH, -NH NHR", R being an alkyl or an aryl radical.

Typical examples, not being however restrictive, of the process according to the present invention may be the preparations of indole from o-ethylaniline, scatole from o-isopropylaniline, benzofuran from o-ethylthiophenol, chinoline from o-propylaniline and the like.

The employed catalyst may consist of a bismuth, molybdenum and vanadium base ternary compound, the preparation of which is carried out according to Italian Pats. Nos. 690,486 and 769,588, or may consist of a mixture of antimony oxide and of an oxide of a metal selected from the ones belonging to the 3rd, 4th, 6th and 8th groups of the periodic system, for example an oxide of La, Ce, Th, Sn, Te, Fe, Co, Ni, U and so on, such catalysts being supported on any carrier known to the skilled in the art, or may be constituted by activated silica.

The catalyst may be employed in a fixed bed, and in a moving or fluid bed.

If activated silica is employed as catalyst in the oxidative catalytic dehydrocyclization of substituted aromatic compounds, it may be employed without additives, or little amounts of other components may be added to it.

For instance, it is possible to add components active as oxidation catalysts selected from oxides or mixtures of oxides of the 3rd, 4th, 5th, 6th and 8th groups of the periodic system, eg oxides or mixtures of oxides of cerium, tin, telluriurn, titanium, phosphorus, arsenic, antimony, bismuth, vanadium, niobium, tantalium, chromium, molybdenum, Wolfram, iron, cobalt or nickel. These additions make very high yields of the sought heterocyclic compound and can be obtained at temperatures lower than the ones required by the only activated silica. They totally have to be lower than 10% b.w. with respect to the silica in order to avoid the combustion reactions to prevail.

The process of the present invention is carried out in presence of oxygen, which may be supplied as such, as air or as any other gas containing oxygen. The molar ratio between oxygen and substituted aromatic compound has to be in the range from 0.2:1 to 5:1. By working at a molar ratio lower then 0.221 the reaction is carried out with low yields, whereas by working at a molar ratio higher than 5:1 the excessive oxidation products are prevailing. A particularly preferred range of oxygen to substituted aromaticcompound molar ratios is the one from An inert diluent is advantageously employed, which diluent may be selected from steam, nitrogen, argon, carbon dioxide, saturated hydrocarbons as n-pentane, isopentane, n-hexane, n-heptane, or any other substance which is not modified by the reaction conditions.

The use of steam in a molar ratio to the aromatic compound comprised in the range from 5:1 to :1 is particularly advantageous.

The process according to the present invention is carried out at a temperature comprised in the range from 350 to 700 C., being the range from 400 to 500 C. particularly preferred.

The reaction pressure may vary in a large range, comprised between mm. Hg and 10 atmospheres, being the process preferred to be carried out at the atmospheric pressure.

The apparent contact time between reactants and catalysts is selected in the range from 0.1 to 10 seconds, being the range from 0.2 to 2.5 seconds particularly preferred.

As apparent contact time between reactants and catalysts we will mean the ratio between the volume of the 3 catalytic bed and the flow of the reactants as gas at the reaction conditions.

The invention will now be illustrated by the following examples, which have not to be understood as restrictive of it. Therein the conversion, selectively and yield terms have to be understood according to the enclosed definitions.

moles of reacted organic compound moles of fed organic compound moles of obtained product moles of reacted organic compound moles of obtained compound moles of fed organic compound EXAMPLE 1 o-Ethylaniline has been contacted with some materials in a stainless steel reactor having the internal diameter of and heated by electric heating, at atmospheric pressure, by feeding o-ethylaniline, air and water at a molar ratio of 1:8:30 and at a contact time of 4. Several proofs were carried out at different temperatures in the SOD-600 C. range. The best results of the selectivity to indole by means of the some materials are reported on Table 1.

Conversion .100

Selectivity 100 very selective in the oxidative dehydrocyclization of o-ethylaniline to indole.

EXAMPLE 3 o-Ethylphenol, air and water were supplied to the same reactor of Example 2, on a 545 cc. catalytic bed of the same catalyst, at atmospheric pressure. At a contact time of 0.8 second, the temperature was varied between 560 and 580 C. and the air/o-ethylphenol molar ratio between 4:1 and6z1, whereas the HgO/O-BthYlPhflHOl molar TABLE 1 o-Ethyl- Products selectivity percent (as Cr) aniline converndole Temp., sion, o-Amino- Ani- Ethylyield, Catalyst 0. percent styrole Indole hne C0-C0: ene percent No catalyst 580 55. 5 43 9. 5 16 Iron shavings.. 570 47.5 20 21. 5 15 Pumice 575 47 11. 5 15. 5 238 59 "ii'' 3i 2 75 SiO 25 Al 0 Z lite 1% x? i 3 505 43.5 27.5 31.5 12 SiO, 555 57.5 p 12.5 20 33.5

The properties of the activated silica as selective catalyst in the oxidative dehydrocyclization of o-ethylamlrne to indole turn out very clear from Table 1.

EXAMPLE 2 A stainless steel reactor having the internal diameter of '%a" and heated by electric heating, was loaded with 390 cc. of silica, having a specific surface of 240 m. /g., which silica having been extruded in the form of little cylinder having a 4 mm. diameter and an 8 mm. length, dried at 150 C. and then calcined in mufiie for 2 hours at 500 C.

o-Ethylaniline, air and water were supplied to the reactor at a pressure little higher than the atmospheric one.

Several proofs were carried out by modifying the temperature, the contact time and the oXygen/o-ethylaniline molar ratio. On the contrary the water/o-ethylaniline molar ratio was kept constant. The obtained results are reported on Table 2.

ratio was kept constant. The results of Table 3 were obtained.

Higher than 50% yields of benzothiophene were obtained by working at the same conditions of Example 3 and by supplying o-ethylthiophenol, air and water to the reactor.

EXAMPLE 5 Some tests were carried out by employing silica at diflerent specific surface. o-Ethylaniline, air and water were TABLE 2 Oz/O- Conver- Selectivity products (as C!) percent ethylon c- Contact aniline, ethyl- Yield time, moles} aniline, o-Amino indole, Average temp., 0. sec. mole percent styrole Indole CO- 00, percent 5 supplied to a stainless steel reactor having the internal diameter of and the catalytic bed of 1 m. at a molar ratio of 1:6:30, at atmospheric pressure, at a temperature of 5 80 C. and at contact time of 1.0 seconds. The results o-Ethylaniline/air/water supplied at a molar ratio of Conversion -ethylaniline 69% are reported on Table 4. 2 1

TABLE 4 Selectivity indole 68% Lslgz. LSih. Bio 2 1 11 0! 1.1 0X 2 Catalyst Cents H AS gel Select1v1ty 0 ammostyrole 12% Specific surface. MJ/g 5 155 240 230 X q Convarsion, o-ethylaniline, per- 46 56 57 35 E MPLE 8 ca a maul-e percent 5 55 5 5 Some tests were carried out by working on a fluid bed.

125 12.5 1L5 13 The working conditions were the following ones: Selectivity 004-002, percent g 1433 1325 Rea t r= mt -=6" h 11 m. Yiel o p Melted Salts heating EMMPLE 6 Loaded cata1yst=l9.2 kg. o-Ethylaniline, air and water, and then o-ethylaniline, Feeding: o o-Ethylanlline, air and water preheated at 500 C. air, water and nitrogen were supplied to a reactor equal H O/o eth lanfline molar ratiO 10.1 to the one of the preceding example, at molar ratios of Atamos g ressure 1:6:30 and 1:6:20z10, by working in presence of a S102 p P Ludox A.S. catalyst, at a temperature of 580 C., at The obtained results are reported on Table 7.

TABLE 1 Average temperature, O.

Linear speed, cm./sec 4 40 40 40 40 4 20 oz/o-ethylaniline,moles/mole--- 1.2 1.3 1.2 1.2 0.5 0.9 1.8 1.3 1.3 Conversion oethylaniline, perce 49 59 60.5 39.5 47 57 53 52 Selectivity indole, percent 59 64 69 69 35 60.5 56 59 Selectivity o-aminostyrole, percent 14 12 11 10 16.5 14.5 14 11.5 16 Selectivity C0 +C0z,pereent- 15.5 15 5 12 11.5 6 11 21 12.5 16 Yield indole, percent 29 41 42 14 28 .32 34 31 EXAMPLE 9 atmospheric pressure and at a contact time of 1 second. The obtained results are reported on Table 5.

Some tests were carried out by working at different TABLE 5 H O/OEA ratios. The working conditions were the fol- Feedin lowing ones: OEA/air/ OEA/air/ Reactor: int. 1 /2 h.= 1.2 1:11.

2 2845 40 Electric heating 51 5 42 5 Loaded catalyst1=100 g. Conversion o-ethylaniline. percent Selectivity indole. percent 54 5 Atmospheric pressure selectiviig 8616110(S}16Y1010.P6I%6Htg Linear speed=6 crn./sec. Selecti apereen Yieldmdole percent 28 13 45 A1r/o ethylaniline molar ratio-6.1

OEA=o-Ethy1anil1ne. The obtained results are reported on Table 8.

TABLE 8 Average temperature, C.

HzO/o-ethylaniline moles/mole 4.5 4.5 10.5 10.5 17 Conversion o-ethy aniline, percent 12.5 20.5 42 44 53.5 54 60 Selectivity indole, percent .5 18 60 61.5 63 56.5 56.5 Selectivity o-arninostyrole, percent 14 18 17 16 12 11 12 Selectiv1tyCO+COz, percent 69 58.5 15 11.5 165 17.5 16.5 Yield indole, percent 2 3.5 25 27 31 34 EXAMPLE 7 EXAMPLE 10 A test on a iiuid bed was carried out; the working conditions and the results are reported on Table 6.

The catalyst was obtained by melting Fe(NO -H O and then by adding little parts of Sb O At the end of the adding of Sb O the reaction mixture was heated up to the disappearance of the introus vapors. The activation was carried out by heating for: 12 hours at C.; 16 hours at 400 C.; 12 hours at 650 C.; 12 hours at 750 C.; and 48 hours at 850 C.

The final composition of the catalyst was the following one:

Fe O 21.5% b.w.

corresponding to a Sb/Fe atomic ratio of 2:1.

EXAMPLE 11 A catalyst consisting of antimony and uranium oxide was prepared according to the following process.

A dust of metallic antimony was dissolved into concentrated HNO and uranyl nitrate was dissolved into water. The two solutions were brought to a pH of about 8 by adding watery ammonia after they had been joined together. The obtained precipitate was filtered and washed by distilled water, then it was dispersed into colloidal silica.

The catalyst was subjected to an atomization and transformed into tablets after the adding of the 30% b.w. of NH HCO then it was calcined in the presence of an air flow for 4 hours at 750 C. The final composition of the catalyst was the following one:

U308: b-W. 813 43.2% b.W. 40.1% b.W.

corresponding to a Sb/U atomic ratio of 4.5 :1.

EXAMPLE 12 TABLE 9 Conversion Contact oethylaniltime ine, percent Selectivity indole, percent Yield indole, percent Average temp.,

EXAMPLE 13 The catalyst of Example 11 was employed in a catalytic bed having a 1 m. height and a 387 cc. volume. o-Ethylaniline, air and water were supplied in a molar ratio of 1:8:50, atatmospheric pressure and at a contact time of Contact time, sec 0. 40 0. 40 Moles Oz/moles o-ethylaniline- Moles H 1 sec. The results reported on Table 10 were obtained by working at two dilferent temperatures.

TABLE 10 Conversion Selectivity Yield Average o-ethylaniline, indole, indole, temp. percent percent percent EXAMPLE 14 gO/moles o-ethylaniline Conversion o-ethylaniline, percent. Selectivity indole percent- Yield indole, percent Yield indole, percent -II 12.5 16 15.5 16

ume. Some tests were carried out by varying the working conditions. The results are reported on Table 11.

TABLE 11 Average temperature, C.

Contact time, sec 1. 10 Moles O zlmoles o-ethylam'line 1. 2 Conversion o-ethylaniline, percen Selectivity indole, percent- 41. 5 3

EXAMPLE 1s o-Ethylaniline, air and water were supplied to a stainless steel reactor having the internal diameter of 'Ms", in presence of a catalytic system consisting of 0.6V205 1131203 '1-6MOO3 TABLE 12 Average temperature, C.

Moles 02/moles o-ethylaniline Moles HzO/moles o-ethylaniline--. Conversion o-ethylaniline, percent Selectivity indole, percent Yield indole, percent EXAMPLE 16 The reaction was carried out at the same conditions of the preceding examples, by working on a catalytic system having the same composition of the preceding example in a bed diluted by inert material in a ratio of 1:4 which bed having a 0.6 7 m. height and a 260 cc. volume. The results are reported on Table 13.

TABLE 13 Average temperature, 0.

EXAMPLE 17 Some tests were carried out on a catalyst consisting of 0.6V O -1Bi O -L6MoO supported on 15% of S102 by working in the same reactor of the preceding examples. The catalytic bed had a 1.21 m. height and a 510 cc. volume. The results reported on Table 14 were obtained by feeding o-ethylaniline, air and Water. The o-ethylaniline/water ratio always was 1:50.

9 EXAMPLE 1:;

Benzofuran was obtained at selectivities higher than 60% and yields higher than 40% by feeding o-ethylphenol, air and water in a molar ratio of 1:830, at 550 C. and at a contact time of 1 sec. and by working on the same catalyst and reactor of Example 17.

EXAMPLE 19 Very high selectivities and yields of benzothiophene were obtained by feeding o-ethylthiophenol, air and water and working at the same conditions of Example 18.

What we claim is:

1. In a process for the oxidative catalytic dehydrocyclization of substituted aromatic compounds of the formula:

10 oxygen-containing gas to substituted aromatic compound ranging from 0.2-1 to 5:1.

2. A process according to claim 1 wherein said temperature is 400-5 00 C.

3. A process according to claim 1 wherein said pressure is atmospheric pressure.

4. A process according to claim 1 wherein it is carried out in presence of a diluent inert.

5. A process according to claim 4 wherein said reaction mixture diluent is selected from steam, nitrogen, argon, carbon dioxide, or saturated hydrocarbons.

6. A process according to claim 1 wherein said molar ratio is .8:1 to 25:1.

7. A process according to claim 1 wherein the substituted aromatic compound is orthoethylaniline.

8. A process according to claim 1 wherein the substituted aromatic compound is orthoethylphenol.

9. A process according to claim 1 wherein the substituted aromatic compound is orthoethylthiophenol.

References Cited UNITED STATES PATENTS 3,441,569 4/1969 Hargis et al. 260-3191 JOSEPH A. NARCAVAGE, Primary Examiner US. Cl. X.R. 

